I just heard about this on TV on the weekend!
If I can remember what they said...

It involves the length of the daylight, the the night temperatures, and the timing of the sap pulling back into the main part of the trees.

so it a combo of these things and also rainfall too that creates the set up for the leaves to change colors.

If the combo & timing is perfect then brilliant colors will be seen but if one or more is off then less chances of wonderful colors.